True or false: "The assumption that the adversary has access to the encryption device is completely unrealistic and useless."

False — this assumption underpins the chosen-plaintext attack, which is not only realistic but always possible against public-key encryption.

Why the assumption is valid:

• In a chosen-plaintext attack, the attacker feeds chosen inputs to an encryption device and observes the outputs
• This is realistic in scenarios like:
  • Capturing an encryption device (e.g., an Enigma machine in WWII)
  • Having temporary access to a system (insider threat, social engineering)
  • Public-key encryption — anyone can encrypt any plaintext using the public key!

Critical insight: For any public-key system, the attacker always has the encryption device (the public key). Therefore, every public-key scheme must be designed to resist chosen-plaintext attacks by default.

The assumption isn't useless — it defines the strongest standard attacker model that every serious cipher must defend against. If a cipher can't resist chosen-plaintext attacks, it's not suitable for public-key use.

Go deeper:

• Chosen-plaintext attack (Wikipedia) — why device access is the realistic standard model.